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https://issues.apache.org/jira/browse/HIVE-23123?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17072779#comment-17072779
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Miklos Gergely commented on HIVE-23123:
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[~jcamachorodriguez] please let me know what you think.
> Export/Import of views and materialized views
> ---------------------------------------------
>
> Key: HIVE-23123
> URL: https://issues.apache.org/jira/browse/HIVE-23123
> Project: Hive
> Issue Type: Bug
> Components: Hive
> Reporter: Miklos Gergely
> Assignee: Miklos Gergely
> Priority: Major
>
> According to
> [https://cwiki.apache.org/confluence/display/Hive/LanguageManual+ImportExport]
> import and export can be done by using the
>
> {code:java}
> export table ...
> import table ...
> {code}
> commands. The document doesn't mention views or materialized views at all,
> and in fact we don't support commands like
>
> {code:java}
> export view ...
> import view ...
> export materialized view ...
> import materialized view ...
> {code}
> they can not be parsed at all. The word table is often used though in a
> broader sense, when it means all table like entities, including views and
> materialized views. For example the various Table classes may represent any
> of these as well.
> If I try to export a view with the export table ... command, it goes fine. A
> _metadata file will be created, but no data directory, which is what we'd
> expect. If I try to import it back, an exception is thrown due to the lack of
> the data dir:
>
> {code:java}
> java.lang.AssertionError: null==getPath() for exim_view
> at org.apache.hadoop.hive.ql.metadata.Hive.loadTable(Hive.java:3088)
> at org.apache.hadoop.hive.ql.exec.MoveTask.execute(MoveTask.java:419)
> at org.apache.hadoop.hive.ql.exec.Task.executeTask(Task.java:213)
> at
> org.apache.hadoop.hive.ql.exec.TaskRunner.runSequential(TaskRunner.java:105)
> at org.apache.hadoop.hive.ql.Executor.launchTask(Executor.java:364)
> at org.apache.hadoop.hive.ql.Executor.launchTasks(Executor.java:335)
> at org.apache.hadoop.hive.ql.Executor.runTasks(Executor.java:246)
> at org.apache.hadoop.hive.ql.Executor.execute(Executor.java:109)
> at org.apache.hadoop.hive.ql.Driver.runInternal(Driver.java:722)
> at org.apache.hadoop.hive.ql.Driver.run(Driver.java:491)
> at org.apache.hadoop.hive.ql.Driver.run(Driver.java:485)
> {code}
> Still the view gets imported successfully, as data movement wasn't even
> necessary.
> If we try to export a materialized view which is transactional, then this
> exception occurs:
>
> {code:java}
> org.apache.hadoop.hive.ql.parse.SemanticException:
> org.apache.hadoop.hive.ql.metadata.InvalidTableException: Table not found
> exim_materialized_view_da21d41a_9fe4_4446_9c72_d251496abf9d
> at
> org.apache.hadoop.hive.ql.parse.AcidExportSemanticAnalyzer.analyzeAcidExport(AcidExportSemanticAnalyzer.java:163)
> at
> org.apache.hadoop.hive.ql.parse.AcidExportSemanticAnalyzer.analyze(AcidExportSemanticAnalyzer.java:71)
> at
> org.apache.hadoop.hive.ql.parse.RewriteSemanticAnalyzer.analyzeInternal(RewriteSemanticAnalyzer.java:72)
> at
> org.apache.hadoop.hive.ql.parse.BaseSemanticAnalyzer.analyze(BaseSemanticAnalyzer.java:289)
> at org.apache.hadoop.hive.ql.Compiler.analyze(Compiler.java:220)
> at org.apache.hadoop.hive.ql.Compiler.compile(Compiler.java:104)
> at org.apache.hadoop.hive.ql.Driver.compile(Driver.java:183)
> at org.apache.hadoop.hive.ql.Driver.compileInternal(Driver.java:601)
> at org.apache.hadoop.hive.ql.Driver.compileAndRespond(Driver.java:547)
> at org.apache.hadoop.hive.ql.Driver.compileAndRespond(Driver.java:541)
> {code}
> So the export process can not handle it, as the temporary table is not
> getting created.
>
> The import command handling have a lot of codes dedicated to importing views
> and materialized views, which suggests that we support the importing (and
> thus also suggests implicitly that we support the exporting) of views and
> materialiezed views.
>
> So the conclusion is that we have to decide if we support exporting/importing
> of views and materialized views.
> If we decide not to support them then:
> - export process should throw an exception if a view or materialized view is
> the subject
> - the codes specific to view imports should be removed
> If we decide to support them, then:
> - the commands mentioned above above should be introduced
> - exception should be thrown if not the proper command used (e.g. export
> view on a table)
> - the exceptions mentioned above should be fixed
> I prefer not to support them, I don't think we should support the exporting /
> importing of views. The point of exporting / importing is the transfer of
> data, not DDL, it causes more issues than it solves. Our current
> documentation also suggests that it is only supported for tables.
>
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